The present invention relates to drip irrigation lines, and particularly to drip irrigation lines which include a plurality of emitter units secured within a water supply tube for discharging water therefrom at a low rate.
Irrigation emitters are commonly constructed with relatively large passageways to reduce the sensitivity of the emitter to clogging by particles in the irrigation water. However, such emitters may also be clogged by external particles, e.g., dirt entering the emitters via the water discharge openings. The problem is particularly acute when a drip irrigation line is emptied since this produces a vacuum within the line which tends to suck external particles into the emitter units via the water discharge openings. For this reason, special pains are frequently taken in installing a drip irrigation line to expose the water discharge openings to the air and not to the soil, but even then, there is still a large tendency of external solid particles to enter the line via the water discharge openings particularly when the line is emptied.
It is known to provide drip irrigation emitters with a one-way valve at the inlet to prevent undesirable discharge or leakage of water when the line pressure is not sufficient for drip irrigation purposes; see, for example, Mehoudar U.S. Pat. Nos. 5,279,462 and Eckstein et al 5,615,838. Such emitters utilize the membranes provided for the function of pressure-compensation also for the function of acting as a one-way valve at the inlet to prevent water discharge or leakage at unduly low line pressures. The fad that the same membrane serves both the one-way valve function, and also the pressure-compensation function, makes it difficult to design it so that it optimally serves both functions for each application.